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Mobo only powers up without the 4pin cpu power plugged in

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January 18, 2009 4:33:06 PM

It's a Foxconn microATX mobo A7GM-S.

When everything is plugged it, no power. When I unplugged the 4 pin cpu connector, the mobo boots up. Fans come on and everything. But nothing on the screen. I changed the power supply to 650 watts from 500.
Any idea what is wrong? bad motherboard??? THANKS

Q-Pack2
A7GM-S
Athlon 64 X2 6000
4GB G SKill Ram
640GB HD
Blu-Ray Drive
a b V Motherboard
a b à CPUs
January 19, 2009 12:30:48 AM

It's always a bad sign when someone mentions a PSU without giving a brand or model.

With the 4-pin plugged in, will the board briefly power up when you unplug the PSU, leave it for a minute, then plug it back in?

Did you install the motherboard standoffs only in those places that correspond to screw holes in the motherboard?

Have you tried with just one stick of RAM installed? What are the specifics of your RAM?

Have you inspected the CPU for bent pins, and foreign material?




January 19, 2009 2:20:35 AM

The PSU is Antec Neopower 650. The original PSU that came with the case is the stock PSU that comes with the Q-Pack2 case.

With the 4-pin plugged in, the board comes up for 2-3 seconds and then fades out. When I switch off and on again on the PSU, nothing happens. If I unplugged the 4-pin, then power on, everything comes on.

Yes, only screws in the correspond holes on the board.
I tried with two, one stick and no sticks.
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory

CPU area and heat sink all clean.

Here's a brief history:

First day: got all the parts and installed in new case. Everything went well. Vista boots up. I was using the blu-ray player. Everything was running fine.

Second day: I decided to use the temp gauge thing that came with the case. It sends the temp of the HD n CPU to the front panel LCD.

So I plugged the power for LCD into the PSU. I taped the ends of the sensor to the HD surface. I taped the sensor to the heat sink of the CPU. Thats when it started not booting up right.

I thought it was the PSU, so I went and got the Antec Neopower 650. But got the same result with the new PSU.

I think I need to get a new board. I was look at RMA for Foxconn, it looks impossible. Newegg is not doing RMA for the board.

Any ideas from the above? THANKS!


Proximon said:
It's always a bad sign when someone mentions a PSU without giving a brand or model.

With the 4-pin plugged in, will the board briefly power up when you unplug the PSU, leave it for a minute, then plug it back in?

Did you install the motherboard standoffs only in those places that correspond to screw holes in the motherboard?

Have you tried with just one stick of RAM installed? What are the specifics of your RAM?

Have you inspected the CPU for bent pins, and foreign material?

Related resources
January 19, 2009 5:20:58 AM

Have you tried re-seating everything??

I tend to look at what you have done... You went inside the case, tinkered, and poof it stopped working. There is a good chance that a cable or card was bumped. If I were you, I would unplug EVERYTHING, pull the motherboard out, and put it back together as you originally had it (without the temp gauge), put NEW thermal compound on the CPU heat sink, while the CPU is out examine the pins carefully.

In fact I would do this exactly, once everything has been unplugged/removed and the motherboard put back in, only plug in the bare minimum for the system to boot up.

Video card (make sure the PCI-E power is supplied to the card, if your card needs it).
1 stick of memory in SLOT 1
CPU 12v power
24pin Motherboard Power
CPU heat sink (Of course!)

If it refuses to make it to the POST screen, try a different Video Card (if you have one). You didn't mention that you were using a video card though, but If you are using a video card, remove it and use the on-board video.

If the system wont boot now try a different stick of memory in SLOT 1.
No boot yet? - Try the same stick in different slots, try them all. If it still wont boot try the other stick in the same manner (different slots). If you have any extra memory anywhere else, give it a try in the same way.

If the system still will not boot after all this, try a different CPU (if you have one). Try the CPU in a different motherboard (if you have one). You mentioned that a different power supply has the same effect, so I doubt that's the problem.

If you don't have extra parts to try I would say it's either the memory, motherboard, or CPU. Hard to say what it is.

If you manage to get it to boot during the process you will be able to find the problem pretty easily. Plug in one component at a time, hard drive try to boot again; if it refuses to boot the hard drive is the problem... etc etc so on and so forth.

Btw - Did you overclock anything at anytime? If so, read your motherboard manual and reset the BIOS. In fact just go ahead and reset the BIOS, it might fix your problem (stranger things have happened).
January 19, 2009 9:39:22 AM

You should really try removing all memory sticks to verify mobo problem. Usually motherboard beeps when memory is not installed. Assuming no problem with board. Board with defects no longer beeps when memory is removed.
a b V Motherboard
a b à CPUs
January 19, 2009 10:20:24 AM

"G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory"

Again, please be more specific. Newegg has about 8 different kits matching this description:
http://www.newegg.com/Product/ProductList.aspx?Submit=E...(PC2%206400)

Some of those might be problematic with your board.

Your system is not booting up. What is happening is that your power comes on with just the 24-pin connected, but the board never actually posts. When you actually connect the CPU power, the board tries to post, fails, and turns itself off.

Memory is always the first suspect in such cases. If you are using a highly volted kit, such as the 2.1V, that might not boot up without a BIOS adjustment first.


"Yes, only screws in the correspond holes on the board."

Not the screws, the standoffs is what I'm interested in. The ONLY place the back of the board should make contact is on the standoffs, and only in the proper places.

I would not have recommended the Neopower. Not a particularly good line from Antec. The Trio, Earthwatts, TPQ, or Signature lines are better. I doubt that's the issue though.

"I taped the sensor to the heat sink of the CPU. Thats when it started not booting up right."
That won't give you a meaningful temp reading anyway. I would certainly unplug the LCD and remove the sensors.

In fact, you should build minimally out of the case at this point, if nothing else has worked... on a cardboard box is good, but not on an anti-static bag as those can actually conduct.

ir_efrem gave you a bunch of good advice.
January 19, 2009 12:02:32 PM

nhkteainc said:


When everything is plugged it, no power. When I unplugged the 4 pin cpu connector, the mobo boots up.


Are you 100% sure that you are not trying to plug a 4 pin PCI-e power connector into it? I have done this before by accident, and it wouldnt power up.
January 19, 2009 6:39:12 PM

If your M/b is 775, check to make sure there is no dirt or fluff caught in the cpu pins.
December 20, 2010 3:51:29 PM

Well, after 6 long months here I am with the exact same problem, but in my case, this PC has been working for over a year, 24/7 on, never had a problem, and yes I build it my self, the only thing that i have change since the first day until Jun 2010 was the AMD X2 chip set, i had replaced now I'm using an X4chip set, but...

a few days ago I went to visit some friends, so I turnoff everything, you know, when you know that you wont be at home for a few day you turn off everything, and unplug everything, but today that I'm back, i wanted to use my PC but just wont turn on, it's on for only a few seconds and it shutoff it self...

i did a manual reset

i toke the video cards and audio card away, and left just the nessecary hardware to turn on but nothing happen
BUT! if I unplug the 4 pin from the PSU it stay on but nothing else happen...
a c 156 V Motherboard
a c 172 à CPUs
December 21, 2010 10:51:36 AM

Work through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...
(This is in Proximon's signature list.)
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

(The rest is an expansion of the troubleshooting techniques in my breadboarding thread (link later).

If not, continue.

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

Make sure you plug the CPU power cable in. The system will not boot without it.

I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card.

Silence or long single beeps indicate a problem with the memory.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.
At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
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